Technical Field
The present invention relates to the networking technology of wireless sensor networks, and more particularly to a lower power consumption networking method of 802.15.4e wireless device that takes power based on 4-20 mA current loop.
Description of Related Art
4-20 mA current loop signal is often used in the industrial environments to realize the remote transmission of measurement data. Information in the Hart protocol communication is transmitted through such signal. The reason why such signal transmission becomes the first choice is that the signal not only is simple, convenient, anti-noise, and safe, but also can be remotely transmitted when no data is corrupted. 4-20 mA is divided into two wire system and three wire system. In the two wire system, the same cable is used for the signal transmission and the power supply so that the cable can provide power supply for wireless devices. However, these devices must consume very low power because the 4-20 mA current loop can only provide quite limited power. The minimum current is only 4 mA in the normal operation of the loop while the current may reach as low as 0 mA when there is a warning or an error. So, it is necessary to control the power consumption in the network when there is limited power obtainable in the loop to ensure that the power consumption is less than or equal to the power obtained in the unit cycle so as to maintain long-term and stable operation of wireless devices.
At present, in addition to high reliability and high real time, low power consumption is also pressing requirement for wireless devices in industrial applications. After industrial wired communication was replaced by industrial wireless communication, energy issues became the focus of attention in the practical application and the improvement of communication protocols as important measures for boosting energy efficiency. In the protocol stack of WSN, the Medium access control (MAC) layer determines the allocation and utilisation of channels and plays an important role in the energy consumption of protocol stack. For this purpose, the TG4e working group (IEEE 802,15.40e) was formally set up in 2008 in order to strengthen the support of IEEE802.15,4-2006 for wireless applications in the industrial field and TG4c to enhance and increase the functionalities of MAC.
Like other general self-organising networks, the IEEE802.15.4e network also processes time synchronization, neighbor discovery, and networking interaction. Among, them, the neighbor discovery is considered as the essence of network formation, which is the basis of the MAC protocol, router discovery, and topology management algorithm. Rapid neighbor discovery has great significance for improving network performance.
In recent years, numerous researchers focus on the development of neighbor discovery, but traditional work concentrates on carrier sense multiple access (CSMA) network which uses single channel. Owing to the mutichannel, a variety of single-channel neighbor discovery methods could not be used directly in the IEEE802.15.4e networks. One fundamental reason accounts for this point is that muti-channel increases uncertainty by directly adding another dimension of channel search in the searching space so networking involves channel searching and neighbor discovery, and this also increases the actual completion time significantly. For example, a simple and practical method from the IEEE802.15.4 network called passive neighbor discovery method PSV which turns on all available channels for neighbor discovery with the longest lasting time of each channel, but it will take a lot of time and energy in the case of the undetermined beacon interval. For reducing the ineffective searching time, the literature had successfully investigated a linear programming method to optimize the time of the neighbor discovery based on the IEEE802.15.4e network slot communication features. The literature also proposed a strategy named OPT which reduced the first, average and maximum channel searching time. However, the method only optimize the searching time without taking the energy consumption into account, and this makes it inapplicable to the energy strictly wireless sensor network. this strategy only listen the beacon frames without taking the general messages into account; in addition, the premise of the realization of the strategy is that the devices had been completed time synchronization and operated in accordance with the slot. However, in practical engineering, the new devices have not been synchronized before joining the network where no time slot exists, so the strategy cannot be directly applied in practical engineering.